Polymethyl methacrylate (hereinafter, also denoted simply as PMMA) as a representative of conventional acryl resin is used for optical films due to its excellent transparency and dimensional stability and low hygroscopicity (as set forth in patent document 1).
However, a PMMA film has had problems such that it is deficient in heat resistance and is easily deformed by use under high temperature or over long duration.
Such problems were essential problems to be overcome not only in a physical property of as a simple substance of a film but also in a polarizing plate or display using such a film. Namely, in a liquid crystal display, a polarizing plate curls along with deformation of the film and is bent, resulting in the change in designed retardation and producing problems such that variation in viewing angle or change in color occurs.
There was proposed a method in which a polycarbonate (hereinafter, also denoted simply as PC) was added to an aryl resin to improve heat resistance, but in such a method, usable solvents are limited and miscibility of resins was insufficient, easily causing milky-whitening and making it difficult to use for an optical film (as set forth in patent document 2).
There was also disclosed a method of introducing an alicyclic alkyl group as a copolymerizing component of an acryl resin or a method in which an intramolecular cyclization reaction is performed to form a cyclic structure in the molecular backbone (as set forth in patent documents 3, 4 and 5).
However, these methods improved in heat resistance but were markedly inferior in brittleness of the film and such deteriorated brittleness promoted deformation of a panel, rendering it difficult to inhibit change in; in addition, these films exhibited a high photoelastic coefficient and yielded an excessive retardation when a stress was applied, therefore, problems such as variation in viewing angle or change in color were not overcome.
It is necessary to control the retardation of transmitted light and its wavelength dispersibility to inhibit decoloring, coloring or the like of a liquid crystal display, so-called color shift and to achieve enhanced contrast in all directions, but such wavelength dependency was not sufficiently controlled by the foregoing film.    Patent document 1: JP 5-119217A    Patent document 2: JP 5-306344A    Patent document 3: JP 2002-012728A    Patent document 4: JP 2005-146084A    Patent document 5: JP 2007-191706A